System and method of providing a self-optimizing reservation in space of compute resources

ABSTRACT

A system and method of dynamically controlling a reservation of compute resources within a compute environment is disclosed. The method aspect of the invention comprises receiving a request from a requestor for a reservation of resources within the compute environment, reserving a first group of resources, evaluating resources within the compute environment to determine if a more efficient use of the compute environment is available and if a more efficient use of the compute environment is available, then canceling the reservation for the first group of resources and reserving a second group of resources of the compute environment according to the evaluation.

PRIORITY CLAIM

The present application is a continuation of U.S. patent applicationSer. No. 10/530,577, filed Apr. 7, 2005, which claims priority to U.S.Provisional Application No. 60/552,653 filed Mar. 13, 2004, the contentsof which are incorporated herein by reference in their entirety.

RELATED APPLICATIONS

The present application is related to U.S. patent application Ser. No.10/530,583, filed Apr. 7, 2005, now U.S. Pat. No. 7,620,706, issued Nov.17, 2009, U.S. Pat. No. 10/530,582, filed Aug. 11, 2006, now U.S. Pat.No. 7,971,204, issued Jun. 28, 2011, U.S. patent application Ser. No.10/530,581, filed Aug. 11, 2006, now U.S. Pat. No. 8,413,155, issuedApr. 2, 2013, U.S. patent application Ser. No. 10/530,576, filed Jul.29, 2008, now U.S. Pat. No. 9,176,785, issued Nov. 3, 2015, U.S. patentapplication Ser. No. 10/589,339, filed Aug. 11, 2006, now U.S. Pat. No.7,490,325, issued Feb. 10, 2009, U.S. patent application Ser. No.10/530,578, filed Nov. 24, 2008, now U.S. Pat. No. 8,151,103, issuedApr. 3, 2012, U.S. patent application Ser. No. 10/530,580, filed Apr. 7,2005, still pending, and U.S. patent application Ser. No. 10/530,575,filed Feb. 4, 2008, now U.S. Pat. No. 8,108,869, issued Jan. 31, 2012.The content of each of these applications is incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to reservations in a cluster or morespecifically to a system and method of providing a self-optimizingreservation in space of compute resources.

2. Introduction

The present invention relates to a system and method of allocationresources in the context of a grid or cluster of computers. Gridcomputing may be defined as coordinated resource sharing and problemsolving in dynamic, multi-institutional collaborations. Many computingprojects require much more computational power and resources than asingle computer may provide. Networked computers with peripheralresources such as printers, scanners, I/O devices, storage disks,scientific devices and instruments, etc. may need to be coordinated andutilized to complete a task.

Grid/cluster resource management generally describes the process ofidentifying requirements, matching resources to applications, allocatingthose resources, and scheduling and monitoring grid resources over timein order to run grid applications as efficiently as possible. Eachproject will utilize a different set of resources and thus is typicallyunique. In addition to the challenge of allocating resources for aparticular job, grid administrators also have difficulty obtaining aclear understanding of the resources available, the current status ofthe grid and available resources, and real-time competing needs ofvarious users. One aspect of this process is the ability to reserveresources for a job. A cluster manager will seek to reserve a set ofresources to enable the cluster to process a job at a promised qualityof service.

General background information on clusters and grids may be found inseveral publications. See, e.g., Grid Resource Management, State of theArt and Future Trends, Jarek Nabrzyski, Jennifer M. Schopf, and JanWeglarz, Kluwer Academic Publishers, 2004; and Beowulf Cluster Computingwith Linux, edited by William Gropp, Ewing Lusk, and Thomas Sterling,Massachusetts Institute of Technology, 2003.

It is generally understood herein that the terms grid and cluster areinterchangeable in that there is no specific definition of either. Ingeneral, a grid will comprise a plurality of clusters as will be shownin FIG. 1A. Several general challenges exist when attempting to maximizeresources in a grid. First, there are typically multiple layers of gridand cluster schedulers. A grid 100 generally comprises a group ofclusters or a group of networked computers. The definition of a grid isvery flexible and may mean a number of different configurations ofcomputers. The introduction here is meant to be general given thevariety of configurations that are possible. A grid scheduler 102communicates with a plurality of cluster schedulers 104A, 104B and 104C.Each of these cluster schedulers communicates with a respective resourcemanager 106A, 106B or 106C. Each resource manager communicates with arespective series of compute resources shown as nodes 108A, 108B, 108Cin cluster 110, nodes 108D, 108E, 108F in cluster 112 and nodes 108G,108H, 1081 in cluster 114.

Local schedulers (which may refer to either the cluster schedulers 104or the resource managers 106) are closer to the specific resources 108and may not allow grid schedulers 102 direct access to the resources.Examples of compute resources include data storage devices such as harddrives and computer processors. The grid level scheduler 102 typicallydoes not own or control the actual resources. Therefore, jobs aresubmitted from the high level grid-scheduler 102 to a local set ofresources with no more permissions that then user would have. Thisreduces efficiencies and can render the reservation process moredifficult.

The heterogeneous nature of the shared resources also causes a reductionin efficiency. Without dedicated access to a resource, the grid levelscheduler 102 is challenged with the high degree of variance andunpredictability in the capacity of the resources available for use.Most resources are shared among users and projects and each projectvaries from the other. The performance goals for projects differ. Gridresources are used to improve performance of an application but theresource owners and users have different performance goals: fromoptimizing the performance for a single application to getting the bestsystem throughput or minimizing response time. Local policies may alsoplay a role in performance.

Within a given cluster, there is only a concept of resource managementin space. An administrator can partition a cluster and identify a set ofresources to be dedicated to a particular purpose and another set ofresources can be dedicated to another purpose. In this regard, theresources are reserved in advance to process the job. There is currentlyno ability to identify a set of resources over a time frame for apurpose. By being constrained in space, the nodes 108A, 108B, 108C, ifthey need maintenance or for administrators to perform work orprovisioning on the nodes, have to be taken out of the system,fragmented permanently or partitioned permanently for special purposesor policies. If the administrator wants to dedicate them to particularusers, organizations or groups, the prior art method of resourcemanagement in space causes too much management overhead requiring aconstant adjustment the configuration of the cluster environment andalso losses in efficiency with the fragmentation associated with meetingparticular policies.

To manage the jobs submissions, a cluster scheduler will employreservations to insure that jobs will have the resources necessary forprocessing. FIG. 1B illustrates a cluster/node diagram for a cluster 124with nodes 120. Time is along the X axis. An access control list 114(ACL) to the cluster is static, meaning that the ACL is based on thecredentials of the person, group, account, class or quality of servicemaking the request or job submission to the cluster. The ACL 114determines what jobs get assigned to the cluster 110 via a reservation112 shown as spanning into two nodes of the cluster. Either the job canbe allocated to the cluster or it can't and the decision is determinedbased on who submits the job at submission time. The deficiency withthis approach is that there are situations in which organizations wouldlike to make resources available but only in such a way as to balance ormeet certain performance goals. Particularly, groups may want toestablish a constant expansion factor and make that available to allusers or they may want to make a certain subset of users that are keypeople in an organization and want to give them special services butonly when their response time drops below a certain threshold. Given theprior art model, companies are unable to have the flexibility over theircluster resources.

To improve the management of cluster resources, what is needed in theart is a method for a scheduler, a cluster scheduler or cluster workloadmanagement system to manage resources in a dimensional addition tospace. Furthermore, given the complexity of the cluster environment,what is needed is more power and flexibility in the reservationsprocess.

SUMMARY OF THE INVENTION

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth herein.

The invention herein relates to systems, methods and computer-readablemedia for optimizing the resources used in a compute environment such asa cluster or a grid. The method aspect of the invention dynamicallycontrols a reservation of compute resources by receiving a request froma requestor for a reservation of resources within the computeenvironment, reserving a first group of resources and evaluatingresources within the compute environment to determine if a moreefficient use of the compute environment is available. If a moreefficient use of the compute environment is available, then the methodcomprises canceling the reservation for the first group of resources andreserving a second group of resources of the compute environmentaccording to the evaluation. The method may also include modifying acurrent reservation of resources to improve the efficient use of theenvironment.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1A illustrates generally a grid scheduler, cluster scheduler, andresource managers interacting with compute nodes;

FIG. 1B illustrates a job submitted to a resource set in a computingenvironment;

FIG. 2A illustrates a concept of the present invention of dynamicreservations; and

FIG. 2B illustrates an embodiment of the invention associated withself-optimizing reservations in space.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

The present invention relates to resource reservations in the context ofa cluster environment. The cluster may be operated by a hostingfacility, hosting center, a virtual hosting center, data center, grid,cluster and/or utility-based computing environments.

Every reservation consists of three major components: a set ofresources, a timeframe, and an access control list (ACL). Additionally,a reservation may also have a number of optional attributes controllingits behavior and interaction with other aspects of scheduling. Areservation's ACL specifies which jobs can use the reservation. Onlyjobs which meet one or more of a reservation's access criteria areallowed to use the reserved resources during the reservation timeframe.The reservation access criteria comprises, in one example, at leastfollowing: users, groups, accounts, classes, quality of service (QOS)and job duration. A job may be any venue or end of consumption ofresource for any broad purpose, whether it be for a batch system, directvolume access or other service provisioning.

A workload manager, or scheduler, will govern access to the computeenvironment by receiving requests for reservations of resources andcreating reservations for processing jobs. A workload manager functionsby manipulating five primary, elementary objects. These are jobs, nodes,reservations, QOS structures, and policies. In addition to these,multiple minor elementary objects and composite objects are alsoutilized. These objects are also defined in a scheduling dictionary.

A workload manager may operate on a single computing device or multiplecomputing devices to manage the workload of a compute environment. The“system” embodiment of the invention may comprise a computing devicethat includes the necessary hardware and software components to enable aworkload manager or a software module performing the steps of theinvention. Such a computing device may include such known hardwareelements as one or more central processors, random access memory (RAM),read-only memory (ROM), storage devices such as hard disks,communication means such as a modem or a card to enable networking withother computing devices, a bus that provides data transmission betweenvarious hardware components, a keyboard, a display, an operating systemand so forth. There is no restriction that the particular systemembodiment of the invention have any specific hardware components andany known or future developed hardware configurations are contemplatedas within the scope of the invention when the computing device operatesas is claimed.

An ACL for the reservation may have a dynamic aspect instead of simplybeing based on who the requester is. The ACL decision making process isbased at least in part on the current level of service or response timethat is being delivered to the requester. To illustrate the operation ofthe ACL, assume that a user submits a job and that the ACL reports thatthe only job that can access these resources are those that have a queuetime that currently exceeds two hours. If the job has sat in the queuefor two hours it will then access the additional resources to preventthe queue time for the user from increasing significantly beyond thistime frame. The decision to allocate these additional resources can bekeyed off of utilization of an expansion factor and other performancemetrics of the job.

Whether or not an ACL is satisfied is typically and preferablydetermined the scheduler 104A. However, there is no restriction in theprinciple of the invention regarding where or on what node in thenetwork the process of making these allocation of resource decisionsoccurs. The scheduler 104A is able to monitor all aspects of the requestby looking at the current job inside the queue and how long it has satthere and what the response time target is and the scheduler itselfdetermines whether all requirements of the ACL are satisfied. Ifrequirements are satisfied, it releases the resources that are availableto the job. A job that is located in the queue and the schedulercommunicating with the scheduler 104A. If resources are allocated, thejob is taken from the queue and inserted into the reservation in thecluster.

An example benefit of this model is that it makes it significantlyeasier for a site to balance or provide guaranteed levels of service orconstant levels of service for key players or the general populace. Bysetting aside certain resources and only making them available to thejobs which threaten to violate their quality of service targets itincreases the probability of satisfying it.

The disclosure now continues to discuss reservations further. An advancereservation is the mechanism by which the present invention guaranteesthe availability of a set of resources at a particular time. With anadvanced reservation a site now has an ability to actually specify howthe scheduler should manage resources in both space and time. Everyreservation consists of three major components, a list of resources, atimeframe (a start and an end time during which it is active), and anaccess control list (ACL). These elements are subject to a set of rules.The ACL acts as a doorway determining who or what can actually utilizethe resources of the cluster. It is the job of the cluster scheduler tomake certain that the ACL is not violated during the reservation'slifetime (i.e., its timeframe) on the resources listed. The ACL governsaccess by the various users to the resources. The ACL does this bydetermining which of the jobs, various groups, accounts, jobs withspecial service levels, jobs with requests for specific resource typesor attributes and many different aspects of requests can actually comein and utilize the resources. With the ability to say that theseresources are reserved, the scheduler can then enforce true guaranteesand can enforce policies and enable dynamic administrative tasks tooccur. The system greatly increases in efficiency because there is noneed to partition the resources as was previously necessary and theadministrative overhead is reduced it terms of staff time because thingscan be automated and scheduled ahead of time and reserved.

As an example of a reservation, a reservation may specify that node002is reserved for user John Doe on Friday. The scheduler will thus beconstrained to make certain that only John Doe's jobs can use node002 atany time on Friday. Advance reservation technology enables many featuresincluding backfill, deadline based scheduling, QOS support, and metascheduling.

There are several reservation concepts that will be introduced asaspects of the invention. These include dynamic reservations,co-allocating reservation resources of different types, reservationsthat self-optimize in time, reservations that self-optimization inspace, reservations rollbacks and reservation masks. Each of these willbe introduced and explained.

Dynamic reservations are reservations that are able to be modified oncethey are created. FIG. 2A illustrates a dynamic reservation. Attributesof a reservation may change based on a feedback mechanism that addsintelligence as to ideal characteristics of the reservation and how itshould be applied as the context of its environment or an entities needschange. One example of a dynamic reservation is a reservation thatprovides for a guarantee of resources for a project unless that projectis not using the resources it has been given. A job associated with areservation begins in a cluster environment (202). At a given portion oftime into processing the job on compute resources, the system receivescompute resource usage feedback relative to the job (204). For example,a dynamic reservation policy may apply which says that if the projectdoes not use more than 25% of what it is guaranteed by the time that 50%of its time has expired, then, based on the feedback, the systemdynamically modifies the reservation of resources to more closely matchthe job (206). In other words, the reservation dynamically adjust itselfto reserve X % fewer resources for this project, thus freeing up unusedresource for others to use.

Another dynamic reservation may perform the following step: if usage ofresources provided by a reservation is above 90% with fewer than 10minutes left in the reservation then the reservation will attempt to add10% more time to the end of the reservation to help ensure the projectis able to complete. In summary, it is the ability for a reservation toreceive manual or automatic feedback to an existing reservation in orderto have it more accurately match any given needs, whether those be ofthe submitting entity, the community of users, administrators, etc. Thedynamic reservation improves the state of the art by allowing the ACL tothe reservation to have a dynamic aspect instead of simply being basedon who the requestor is. The reservation can be based on a current levelof service or response time being delivered to the requestor.

Another example of a dynamic reservation is consider a user submitting ajob and the reservation may need an ACL that requires that the only jobthat can access these resources are those that have a queue time that iscurrently exceeded two hours. If the job has sat in the queue for twohours it will then access the additional resources to prevent the queuetime for the user from increasing significantly beyond this time frame.You can also key the dynamic reservation off of utilization, off of anexpansion factor and other performance metrics of the job.

The ACL and scheduler are able to monitor all aspects of the request bylooking at the current job inside the queue and how long it has satthere and what the response time target is. It is preferable, althoughnot required, that the scheduler itself determines whether allrequirements of the ACL are satisfied. If the requirements aresatisfied, the scheduler releases the resources that are available tothe job.

The benefits of this model is it makes it significantly easier for asite to balance or provide guaranteed levels of service or constantlevels of service for key players or the general populace. By settingaside certain resources and only making them available to the jobs whichthreaten to violate their quality of service targets it increases theprobability of satisfying it.

FIG. 2B illustrates another aspect of the invention, which is thedynamic, self-optimizing reservation in space. This reservation seeks toimprove the efficient use of the compute resources. This is in contrastto a reservation that may self-optimize to improve a response time forjobs submitted by the reservation requestor. As shown in FIG. 2B, themethod comprises receiving a request from a requestor for a reservationof resources within the compute environment (210), reserving a firstgroup of resources (212), evaluating resources within the computeenvironment to determine if a more efficient use of the computeenvironment is available (214) and determining if a more efficient useof the compute environment is available (216). If a more efficient useof the compute environment is available, then the method comprisesmodifying the reservation for the first group of resources to reserve asecond group of resources of the compute environment (218). Themodification may comprise canceling the first reservation and making asecond reservation of a second group of resources that is more efficientor the modification may comprise maintaining the current reservation butchanging the resources reserved.

The reservation may be identified as self-optimizing either by thesystem, by a policy or by the requestor. The self-optimizingclassification may further mean that it is self-optimizing in terms ofthe efficiency of the compute resources or in some other terms such asimproved time to process jobs.

The compute environment is one of a cluster environment, gridenvironment or some other plurality of computing devices, such ascomputer servers that are networked together. The reservation for thefirst group of resources and the reservation for the second group ofresources may overlap in terms of time or resources (space).

The request for resources may include a required criteria and apreferred criteria. The criteria may based cost-based (least expensive)time based (fastest processing time) and so forth. It is preferred thatthe reservation of the first group of resources meets the requiredcriteria and the evaluation of resources within the cluster environmentdetermines if use of the resources in the compute environment can beimproved further comprises evaluating resources to determine if at leastone of the preferred criteria can be met by modifying the reservation ofresources.

The determination of whether the use of the compute environment can beimproved can include a comparison of a cost of canceling the first groupof resources and reserving the second group of resources with theimproved use of the compute environment gained from meeting at least oneof the preferred criteria. In this case, if the cost of canceling thereservation of first group of resources and reserving the second groupof resources is greater than improved usage of the compute environmentgained by meeting at least one of the preferred criteria, then thereservation of first group of resources is not cancelled. A thresholdvalue may be established to determine when it is more efficient tocancel the reservation of first group of resources and reserve thesecond group of resources to meet at least one of the preferredcriteria.

Embodiments within the scope of the present invention may also includecomputer-readable media for carrying or having computer-executableinstructions or data structures stored thereon. Such computer-readablemedia can be any available media that can be accessed by a generalpurpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to carryor store desired program code means in the form of computer-executableinstructions or data structures. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or combination thereof) to a computer, the computerproperly views the connection as a computer-readable medium. Thus, anysuch connection is properly termed a computer-readable medium.Combinations of the above should also be included within the scope ofthe computer-readable media.

Computer-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Computer-executable instructions also includeprogram modules that are executed by computers in stand-alone or networkenvironments. Generally, program modules include routines, programs,objects, components, and data structures, etc. that perform particulartasks or implement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of the program code means for executing steps of the methodsdisclosed herein. The particular sequence of such executableinstructions or associated data structures represents examples ofcorresponding acts for implementing the functions described in suchsteps.

Those of skill in the art will appreciate that other embodiments of theinvention may be practiced in network computing environments with manytypes of computer system configurations, including personal computers,hand-held devices, multi-processor systems, microprocessor-based orprogrammable consumer electronics, network PCs, minicomputers, mainframecomputers, and the like. Embodiments may also be practiced indistributed computing environments where tasks are performed by localand remote processing devices that are linked (either by hardwiredlinks, wireless links, or by a combination thereof) through acommunications network. In a distributed computing environment, programmodules may be located in both local and remote memory storage devices.

Although the above description may contain specific details, they shouldnot be construed as limiting the claims in any way. Other configurationsof the described embodiments of the invention are part of the scope ofthis invention. Accordingly, the appended claims and their legalequivalents should only define the invention, rather than any specificexamples given.

I claim:
 1. A method comprising: reserving a first group of computeresources within a compute environment based on a request for thecompute resources to yield a reservation of the first group of computeresources, the first group of compute resources having a first valuethat is used to determine a threshold value; evaluating the computeenvironment to determine a second value for a second group of computeresources within the compute environment; comparing the second value ofthe second group of compute resources with the threshold value to yielda determination; and if the determination indicates that the secondvalue of the second group of compute resources is an improvement overthe threshold value, then modifying the reservation from the first groupof compute resources to the second group of compute resources of thecompute environment.
 2. The method of claim 1, wherein the computeenvironment is one of an enterprise compute farm, a cluster and a grid.3. The method of claim 1, wherein the request further comprises apreferred criterion and a required criterion.
 4. The method of claim 3,wherein the evaluating further comprises identifying compute resourcesthat are available and meet explicit or implicit preferred criteria ofthe reservation.
 5. The method of claim 4, wherein available computeresources comprise compute resources in an up state with no partial orcomplete failure.
 6. The method of claim 1, wherein modifying thereservation further comprises at least one of canceling the reservationand creating a new reservation, dynamically modifying attributes of anexisting reservation, and dynamically modifying attributes of the firstgroup of compute resources to better satisfy the reservation.
 7. Themethod of claim 1, wherein the reservation for the first group ofcompute resources and a second reservation for the second group ofcompute resources overlap.
 8. The method of claim 3, wherein thereservation of the first group of compute resources meets the requiredcriterion.
 9. The method of claim 8, wherein evaluating computeresources within the compute environment further comprises determiningif at least one of the preferred criteria can be met by modifying thefirst group of compute resources allocated for the reservation.
 10. Themethod of claim 9, wherein the evaluating comprises a comparison of acost of migrating the reservation from the first group of computeresources to the second group of compute resources with an improvedresource allocation gained from meeting at least one of the preferredcriterion.
 11. The method of claim 10, wherein the reservation is notmodified if the cost of modifying the reservation from the first groupof compute resources to the second group of compute resources is equalto or higher than either the threshold value or the improved resourceallocation of the compute environment gained by meeting at least one ofthe preferred criteria.
 12. The method of claim 10, wherein theevaluating further uses a per-reservation policy.
 13. The method ofclaim 12, wherein the per-reservation policy is at least one of anadministrator policy, a user-based policy, a policy of never taking anaction, a policy of always taking an action and a cost-based policy. 14.The method of claim 1, wherein the request is identified as aself-optimizing request.
 15. The method of claim 14, wherein a requestorof the request identifies the request as self-optimizing.
 16. The methodof claim 14, wherein the request is identified as self-optimizing inspace.
 17. The method of claim 14, wherein a requestor of the request ischarged more for a self-optimizing request relative to a charge for anon-self-optimizing request.
 18. A system comprising: a processor; and acomputer-readable storage medium storing instructions which, whenexecuted by the processor, cause the processor to perform operationscomprising: reserving a first group of compute resources within acompute environment based on a request for the compute resources toyield a reservation, the first group of compute resources having a firstvalue that is used to determine a threshold value; evaluating thecompute environment to determine a second value for a second group ofcompute resources within the compute environment; comparing the secondvalue of the second group of compute resources with the threshold valueto yield a determination; and if the determination indicates that thesecond value of the second group of compute resources is an improvementover the threshold value, then modifying the reservation from the firstgroup of compute resources to the second group of compute resources ofthe compute environment.
 19. A non-transitory computer-readable mediumstoring instructions which, when executed by a computing device, causethe computing device to perform operations comprising: reserving a firstgroup of compute resources within a compute environment based on arequest for the compute resources to yield a reservation, the firstgroup of compute resources having a first value that is used todetermine a threshold value; evaluating the compute environment todetermine a second value for a second group of compute resources withinthe compute environment; comparing the second value of the second groupof compute resources with the threshold value to yield a determination;and if the determination indicates that the second value of the secondgroup of compute resources is an improvement over the threshold value,then modifying the reservation from the first group of compute resourcesto the second group of compute resources of the compute environment.